The present invention relates to a method and apparatus for analyzing acquired scan data, and to a scanning fluorescence microscope implementing a method for analyzing acquired scan data. More particularly, the invention relates to a method for acquiring and processing signals of a process which are not directly observable because of the multiplicative superposition of a global interference signal.
In microscopy (cf. C. R. Bright et al., Methods in Cell Biology; Vol. 30, pages 157 to 192, Academic Press Inc.) and cytofluorometry, two identically interfered signals, from which a conclusion as to the desired signal must be drawn, are acquired. During the observation of physiological processes, the physiological and phototoxic processes are superimposed. Similar situations happen in optical measurements using the kind of illumination in which the noise of the light source falsifies the object measurement, or in multispectral image processing, where individual features can be emphasized by reducing multiplicative influences (cf. Jain (1989): xe2x80x9cFundamentals of Digital Image Processing,xe2x80x9d London, Prentice-Hall).
Many processes cannot be observed directly. This is true in particular of processes on which a global interference signal is multiplicatively superimposed. The procedure according to the existing art is to acquirewhenever physically possible two signals I1 (t) and I2 (t) (represented here as time signals). S(t) is the interference signal, F(I(t)) is the detector signal having a first wavelength, and G(I(t)) is the detector signal that derives from a second wavelength.
I1(t)=S(t)F(I(t)) 
I2(t)=S(t)G(I(t)) 
Creating a ratio   r  =                    I        1                    I        2              =                            F          ⁡                      (            I            )                                    G          ⁡                      (            I            )                              =              H        ⁡                  (          I          )                    
which ratio provides more characteristic information about the I than in other cases which cannot be accurately observed. The effect of noise (noise, offsets) is ignored in the case of the two acquired signals I1 (t) and I2 (t). Ignoring the noise results in an additional additive noise term for r, which is ignored here. This type of procedure is existing art, e.g. is utilized in European Patent EP-B-0 592 089, and will be referred to hereinafter as xe2x80x9cratiometric measurement.xe2x80x9d
It is the object of the invention to provide an apparatus which performs an adapted coding of signal pairs.
A further object of the invention is to provide a method implementing an adapted coding of signal pairs.
The configuration according to the present invention provides an advantage that in the context of the transformation, a separation is performed between the usable signal and the interference signal. This considerably simplifies the configuration of the apparatus, resulting in lower manufacturing costs. What is significant in this context is that after the transformation, only scalar variables are processed. The transformation maps the original two-dimensional signal space onto a compact region in a one-dimensional signal space, thereby achieving particular compactness. Because of this property, the usable signal can be coded and memory space is efficiently economized.
Even if the above-described functionality is confined to the ratiometric information, the system of the present invention performs much better than that with purely ratiometric approaches. The polar coordinate transformation maps the relevant measured data onto a particular angle in compact fashion, taking into account the degrees of freedom of the process. Methods based on divisions do not offer this compact transformation or the compression property (linear, in the transformation space) associated therewith.
It should also be noted that the transformation into polar coordinates technically does not necessarily require a division (neural networks, COORDIC algorithms, lookup tables), and represents much more of the underlying mathematical operation than is disclosed in EP-B-0 592 089.